Annan said he will now meet with President Mwai Kibaki and opposition leader Raila Odinga to try to spur progress.

"I hope people will understand this is a move intended to speed up action," Annan said in announcing that he was calling off the talks.

The negotiations have failed to resolve the dispute between Kibaki and Odinga, who says the Dec. 27 presidential election was a sham. Kibaki was declared the winner but international and local monitors say the results were manipulated, making it unclear who would have won.

Kenya was once a beacon of stability in a tumultuous region but the contentious vote sparked widespread fighting as both sides claimed victory. Violence has largely subsided in recent weeks, but attacks that left more 1,000 dead and forced 600,000 from their homes have left the country on edge and worried about the potential for more unrest.

Kibaki was declared the winner of a second five-year term after Odinga's lead in polls evaporated overnight.

Much of the postelection violence has been ethnic, between supporters of Kibaki, a Kikuyu, and groups who back Odinga, a Luo.

The suspension of talks came as international pressure mounted and the opposition threatened to resume nationwide protests this week. Previous protests have turned violent, with dozens killed as police forced back the crowds.

U.S. Secretary of State Condoleezza Rice issued a statement saying the delays were inexcusable.

"There can also be no excuse for violence, and those responsible must be held accountable," she said.

Rice also issued a veiled threat, saying the U.S. relationship with any future Kenyan political leadership was at stake.

"I want to emphasize that the future of our relationship with both sides and their legitimacy hinges on their cooperation to achieve this political solution," Rice said.

Annan said late Monday that almost no progress had been made in the talks.

"I had to conclude that they were not capable of resolving the outstanding issues," he said. Annan said the mediation team "has done its work. I'm now asking the party leaders ... to do theirs."

Tanzanian President Jakaya Kikwete, the current head of the African Union, was scheduled to arrive in the Kenyan capital today to "give support to the mediation process," said his spokesman Premy Kibanga. He said the Tanzanian president will meet with Kibaki, Odinga and Annan.

Negotiators for Kibaki and Odinga had agreed in principle to create a new prime minister's post for the opposition, but sticking points remained over just how much power such a post would carry.

Still, government officials had maintained that they continued to inch closer to a deal.

"We've agreed on some issues," Foreign Affairs Minister Moses Wetangula said after a morning negotiating session, declining to give details. "The more we talk the more we get closer to agreeing," he said.